Liquid crystalline polyester resin has excellent characteristics such as heat resistance, fluidity and electrical characteristic, and is extending its demand mainly on small-sized precision molded products in electric and electronic fields. Its thermal stability and high thermal dimensional precision have been focused and studied on to apply to a supporting base member of heat-generating parts, such as supporting base member of liquid crystal display for Office Automation equipment or cellular phone and lamp components.
To manufacture liquid crystalline polyester resin pellets, a strand group is most generally discharged through a die head having a valve and a discharge port having die holes and is cooled to solidify, and then is cut with a cutter. However, the liquid crystalline polyester resin tends to arrange molecules along the flow direction of melted resin unlike other thermoplastic resins and its melt viscosity may decrease particularly at a low shear rate. Further, its high melting point may require to keep a high temperature of the die head, so that the polymer remaining in the die head is highly crystallized through heat history before being discharged for the next batch or is carbonized to make foreign substance, which might increase to block the die to deteriorate continuous productivity and discharging performance. Furthermore, because the discharged strand group of liquid crystalline polyester resin has a high crystallization rate and cannot be drawn easily, the strand group may meander or flutter. That tendency would become remarkable with many die holes, so that irregular-shaped pellets such as slant pellet, interconnected spherical pellet and uncut pellet is generated to cause a feed rate variation and a blocking at a feeder of extruder or molding machine and feed rate variation.
Patent documents 1 and 2 disclose methods for improving the discharge stability and pellet quality by cutting the strand discharged from the die with a cutter at specific ranges of shear rate, take-up velocity of strand group and average discharge rate of liquid crystalline polyester resin per die hole.
Patent document 3 suggests a method for preparing uniformly-shaped liquid crystalline polyester resin pellets by cooling the strand of liquid crystalline polyester resin discharged from the die below a predetermined temperature.
On the other hand, Patent document 4 suggests a method for preparing uniform polymers by regulating a passing resistance of polymer through a distributor as a general die head for extrusion molding polyester.